Secondary batteries such as nickel-cadmium batteries, nickel-hydrogen batteries, and lithium-ion batteries have been widely used in electronic instruments and electronic components, particularly in mobile phones, notebook personal computers, video camcorders, artificial satellites, electric or hybrid cars, and the like. Conventionally, cases including nickel-plated cold-rolled steel sheets or plastic cases have been used in secondary batteries using strongly alkaline electrolytes, such as nickel-cadmium batteries and nickel-hydrogen batteries. Batteries using non-aqueous electrolyte, such as lithium-ion batteries, have also been used in the state of wrapping non-aqueous electrolytes put into aluminum pouches in plastic cases or in nickel-plated steel sheet or stainless steel sheet cases.
Reductions in the sizes and weights of secondary batteries have been demanded with reductions in the sizes of electronic and electrical components in recent years. In such trends, attention has been focused on thinning of secondary battery containers as a tool enabling larger quantities of electrolytic solutions and active materials to be put in limited capacities, whereby battery capacities can be increased. However, decreases in the strength of the containers due to the thinning cause a risk that external force or stabbing allows the containers to be deformed or broken, thereby resulting in leakage of the electrolytic solutions which are contents. The leakage of the electrolytic solutions has a high probability of seriously damaging apparatuses in which secondary batteries are put. Therefore, the strength of such a container having a wall thickness of 200 μm or less is insufficient in a case in which the member of the container is plastic or aluminum. Thus, a material having a high strength is required for further thinning the container. It is preferable that the material is a general-purpose material in consideration of mass production.
Examples of materials satisfying such demand characteristics include stainless steel foils. The stainless steel foils are foils obtained by thinning stainless steels to have thicknesses of 200 μm or less. The tensile strengths and Vickers' hardnesses of such metal foils are commonly from 2 to 10 times those of plastic or aluminum, and the metal foils have high strengths. Therefore, the metal foils are promising as materials for thinning secondary battery containers.
In recent years, production of an improved stainless steel foil in which a metal chromium layer and a hydrated chromium oxide layer are homogeneously formed on a surface of a stainless steel foil in order to satisfy severe use conditions demanded in the field of electronics has been attempted (Patent Literature 1).
However, such stainless steel foils have been poor in corrosion resistance in electrolytic solutions, and have been able to be corroded due to non-aqueous electrolytic solutions in the case of using the stainless steel foils in the housings and lead wires of batteries. Thus, a metal foil in which an acid-modified polyolefin resin layer with a barrier property against a substance responsible for corrosion is layered on an aluminum foil subjected to chromium-based surface treatment such as trivalent chromium treatment or chromate treatment is disclosed as a manner of compensating for weakness in the corrosion resistance of such metal foils (Patent Literature 2).
Attempts to improve the workability and corrosion resistance of stainless steel foils have been made as described above. However, conventional stainless steel foils have been often insufficient in view of costs and resistance to non-aqueous electrolytic solutions, and a thin stainless steel foil having excellent resistance to an electrolytic solution has been demanded.    Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. H07-62596    Patent Literature 2: JP-A No. 2000-357494